Unraveling the Unusual Chemistry of the Hydrogen-Peroxide-Driven Hypergolic Ignition of a Cyanoborohydride Ionic Liquid as a Next-Generation Green Space Propellant.

Hypergolic ionic liquids (HILs) have emerged as promising self-igniting green space propellants in combination with an oxidizer, replacing toxic hydrazine family rocket fuels. Despite numerous new HILs being reported in the literature, there is no systematic study addressing the key reaction mechanism of such hypergolic ignition. Here, the first comprehensive molecular level understanding of this ignition reaction is revealed, exploring a 1-ethyl-3-methylimidazolium cyanoborohydride-hydrogen peroxide ([EMIM][CBH]-H₂O₂) green bipropellant pair by a novel chirped-pulse droplet-merging technique in a controlled environment. Mechanistically, the anion [CBH]^- triggers the hypergolic ignition through facile exoergic oxidation of the boron center yielding boron dioxide (BO₂) in a barrierless termolecular reaction with two molecules of H₂O₂, followed by an enhanced reactivity of the cation [EMIM]⁺, as evidenced from the excess yield of carbon dioxide (CO₂) and evaluated decay rate constants of [EMIM]⁺ in situ during the droplet-merging reaction.